How do sorghum DDGS stack up with corn co-products and soybean meal in terms of digestibility?
By: Jill Anderson, Alvaro Garcia, and Bobbi J. Wild, SDSU Extension
Sorghum (milo) is gaining notice because it is a more drought tolerant crop compared to corn. In parts of the southern Great Plains sorghum grain is currently used as a renewable fuel source for ethanol production. Using sorghum for ethanol results in the availability of the co-product sorghum distillers dried grains with solubles (SDDG). Research has shown that protein degradation is lower in sorghum grain compared to corn. However, how the protein in SDDG is utilized compared to corn ethanol co-products, and if SDDG could potentially be fed to ruminants at similar dietary inclusion rates as corn DDG still needs to be addressed. Therefore, in this experiment the objective was to determine dry matter (DM) and crude protein (CP) ruminal degradability and intestinal digestibility of SDDG compared to soybean meal and other corn co-products. To meet this objective feed samples were incubated (in situ) in the rumen of three mid-lactation, multiparous, ruminally-cannulated Holstein cows (see Figure 1.) (Body weight: 1754 ± 171 lbs). Five feedstuffs were evaluated: sorghum distillers dried grains (SDDG), corn distillers dried grains (CDDG), reduced-fat corn distillers dried grains (RFDDG), corn gluten meal (CGM) and soybean meal (SBM). Duplicate samples were weighed into small nylon bags and incubated in the rumen for 0, 2, 4, 8, 16, 24 and 48 h. Six additional replicates from each feedstuff were ruminally incubated at 16 hours and residues were used to determine the intestinal digestibility of CP in vitro (in the laboratory- see Figure 2.). Residues were incubated in a Daisy II incubator (Ankom Technology, Inc. Macedon, NY) with pepsin and pancreatin solutions for 1 hour and 24 hours, respectively.
Results demonstrated (see Table 1) that ruminally-degradable DM was less in CGM and greater in CDDG, RFDDG SBM compared to SDDG. Ruminally degradable protein (RDP) was greater in SBM, CDDG, and RFDDG compared to SDDG and CGM. Conversely, ruminally undegradable protein (RUP) was greater in SDDGS and CGM than in SBM, CDDG, and RFDDG. Estimated intestinally degradable protein, intestinally absorbable dietary protein (protein that escapes the rumen and can be digested in the intestine), and total digestible protein were least in SDDG compared to the other feeds. Results indicate crude protein from SDDG was less ruminally degradable and intestinally digestible compared to CDDG, RFDDG, and SBM. Concentrations of RDP and RUP were similar in SDDG and CGM; however, CGM had more total crude protein, intestinally digestible protein, and total digestible protein as a % of total DM. The results indicate that though SDDG is still a viable source of dietary protein for cattle, it behaves differently and has different utilization by dairy cattle than corn co-products. When formulating ruminant diets these differences must be considered to maintain cattle performance.
Notes and Acknowledgements
This research was an undergraduate project for academic credits by Bobbi J. Wild with advisor Jill Anderson, Ph.D. Assistant Professor in the Dairy Science Department. This past spring (April 2015) Bobbi won both a local medal and a regional prize, 2nd place North America, and 1st place United States in the 2015 Alltech Young Scientist Undergraduate competition for her research paper on this project titled “Ruminal degradability and intestinal digestibility of sorghum distillers dried grains compared to corn co-products and soybean meal.” This research was supported by the SDSU Agricultural Experiment Station.